In a packet-switched data communication network, a mobile node (MN) has plural communication interfaces, and uses these communication interfaces to connect to the same correspondent node (CN).
In this case, the MN can switch the communication interface used for communication from one communication interface to another for the purposes of power savings and use of a network interface with low communication cost, for example.
For connection to a network access point, the MN needs to activate an interface in a dormant state to scan available networks. Then, the MN needs to wait for a sync signal and further for a channel access time slot to request channel/time slot resources.
In this case, the MN first activates the interface to synchronize a clock with the access point, then monitors a beacon of the access point on a steady basis to obtain information on a conflict of transmission time allocated to an MN newly participating in the network, and finally registers with the access point in a transmission slot based on the conflict.
In the meantime, as described in Non-Patent Document 1 cited below, a technique for integrating wireless media to enable handover between heterogeneous networks (for example, between 3GPP and WLAN (Wireless Local Area Network or Wireless LAN)) has been recently developed. In this handover process, the MN basically has plural heterogeneous network interfaces so that it can change the interfaces used for efficient communication depending on a variety of circumstances.
Non-Patent Document 1: IEEE P802.21 Specification Draft 02.00, September 2006.
Non-Patent Document 2: 3GPP TS 36.300v8.3.0“3rd Generation Partnership Project; Technical Specification Group Radio Access Network and Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Overall description, Stage 2,” 2007-12.
Non-Patent Document 3: 3 GPP TSG-RAN WG3#56 Tdoc R3-070780 “Network transport QoS for Home NodeBs (HNB),” 2007-05.
In view of the above issue, when an interface of the MN connects to a network access point, the MN first needs to receive a broadcast message such as a beacon in order to acquire information. The beacon is typically transmitted in predetermined cycles, so that the MN needs to wait for about one cycle (a few cycles in some cases) from when the MN starts to receive the beacon until it acquires necessary information. In other words, the MN needs to keep the originally dormant interface active for a longer period, causing a problem that increases power consumption.
When the MN has plural interfaces and receives data through another interface during this period, the MN needs to leave the interface active until the dormant interface is completely connected to the network access point.
In other words, when interfaces are switched, both interfaces need to remain activated simultaneously, resulting in significant consumption of battery power of the MN. On the other hand, if the active interface is turned off before complete connection to and registration with another network access point through the dormant interface to avoid consumption of battery power, the service to the MN may shut down, and hence the quality of service (QoS) may be interrupted.